In traditional milking with manual handling of the equipment a large number of cows are milked simultaneously one to four hours every morning and night. After each milking a manual adjustment is made wherein teat cups used to collect milk from the cows are placed on teat dummies. Rinsing water and later a detergent solution, is sucked from a washing machine through the teat dummies into the teat cups, and onwards through the milking equipment. The fluid transport is driven by a vacuum suction, for instance at an underpressure of 50 kPa, to a collecting chamber, usually called an end unit. Many different vacuum-driven milk transport arrangements have been disclosed, such as U.S. Pat. No. 4,432,700, GB 2095088 and DE 3422452 by WESTFALIA SEPARATOR AG, and DE 2548601 by Miele, which are hereby incorporated by reference.
Generally, the end unit comprises a pump, transporting fluid against the pressure difference out towards the atmospheric pressure. The pipe connection, which during milking is connected to the cooling tank, is moved out of the cooling tank before washing, into a cleaning sleeve. The cleaning sleeve has an output, which is connected to the washing machine. A closed cleaning loop is thus obtained for cleaning in place (CIP). The technique known as CIP is inherited from the dairy industry, and is intended to indicate that rinsing water and detergent solution are circulated through tanks, pipes and process lines without the equipment having to be dismantled.
For the traditional milking equipment, a cleaning loop is formed by manually disconnecting the milk line system from the milk-cooling tank and connecting it to a cleaning fluid system. The milk tank itself is cleaned separately after having been emptied.
When using so called voluntary milking systems, VMS, the milking plant is in operation all hours of the day, having milk stored and transported through pipe systems and tanks. There are thus no natural breaks in the milking providing the opportunity to traditional cleaning or washing. This makes it necessary to divide the milking plant into sub-systems, which are cleaned separately on different times. The only exception, which can be anticipated, is a common cleaning of the entire plants each time the cooling tank has been emptied. Since the tank is generally emptied with an interval of two days, the cleaning frequency is obviously inadequate.
As examples of such sub-systems, the following can be mentioned:
Teat rubbers are rinsed and sometimes disinfected between every cow that is: milked. The water that is used must not leak into the milk.
The quality of the milk is supervised for each milked cow, generally by inspecting the so-called pre-milk, obtained from the teat cavity from the animal. If the milk does not meet up to standards, all the milk from the present cow has to be dumped. All parts of the equipment that has been in contact with the milk are washed afterwards.
The pipe system of the milk line system, comprising pipes and valves, transporting milk from the robot to the cooling tank, often about 20 to 30 meters, needs to be washed a couple of times each day in order to prevent bacterial growth on surfaces that have been in contact with the milk.
Between robot and milking tank there is often a milk filter that has to be changed or washed several times a day, at the same time as the filter housing is washed.
A VMS plant can consist of one milking station only, but for larger plants a number of stations are by necessity working in parallel, but which can be cleaned individually.
In some type of plants the cooling tank is washed separately after being emptied. The milk that is produced during the cleaning of the milking tank is then temporarily stored in a buffer tank. The buffer tank is emptied and washed once the cooling tank is taken back into operation.
The division into separately cleaned sub-systems provides a need for a security system preventing mixture of detergent solution into the milk even if a system separating valve should leak.
In dairy industries the same problem was earlier solved by removing a piece of pipe between parts of the equipment that were washed and parts that contained milk. A similar procedure is used in traditional milking plants. The connection pipe or hose, from the milk-line system to the milk cooling tank is moved manually to a cleaning fluid supply connection for washing.
When the demand for automation made manual pipe removing in dairy industries impossible an analogue solution was developed in the form of valves. System separating valves were used in doubles and were provided with a drained pipe extension in between. In practice, a closing valve was used combined with a three-way valve. The latter opened for drainage of the intermediate pipe when the valves closed of the milk supplies. Later developments originating from the dairy industry has provided double seat valves with a different types of drained chambers between the seats. A drawback for the solutions provided for the dairy industry is that unwashed parts of the equipment are obtained between the sub-systems. The pipe system in a dairy is however enough extensive to provide possibility to shift between different sections so that also border zones are washed. For double seat valves of the “mixed proof” type one has often the possibility of washing and steam sterilising the mid chamber.
Milking plant systems, however, must for a foreseeable future, due to economical reasons if no other, be much simpler. Therefore the basic problem of preventing mixture of detergent into the milk has to be solved in another way.